Alternating optical frequency transfer regenerative repeater system and method without out-of-band noise

Abstract

The application discloses an out-of-band noise-free alternate optical frequency transfer regenerative relay system and method, which can realize relay regeneration and amplification of the optical signal received by the upper link, and the regenerated signal continues to be transmitted to the next regenerative relay or user terminal output. The proposed relay structure can lock the regenerated light source. Meanwhile, the next stage actively compensates the phase noise introduced by the optical signal in the optical fiber link through a servo control module, so that the phase compensation of the received signal light is realized. Through the alternate repetition cascade of the proposed relay structure, the local optical frequency signal can be transmitted for a long distance, so that the user terminal obtains the phase-stable optical frequency signal. The application reduces the asymmetry of the transmission structure by adopting an online Faraday rotator, effectively avoids the influence of the out-of-band path noise, and has the advantages of simple system structure, low overall noise and long transmission distance without using a complex temperature control system.

Description

TECHNICAL FIELD

[0001] The present invention relates to optical frequency transfer, and in particular to an all-pass optical frequency transfer regenerative repeater system and method. BACKGROUND

[0002] High-precision time and frequency standards play an important role in time and frequency metrology, satellite navigation, radio astronomy and fundamental physics research, and are important means for developing scientific research and safeguarding national defense. In many applications, high-precision frequency signals need to be transmitted to remote ends. In order to ensure that the frequency signals of the original sending end can be faithfully reproduced at the remote receiving end, a transfer means with higher precision than the optical frequency standard signal is indispensable.

[0003] In 2010, Lopez et al. of University of Paris 13 in France used a cascaded transmission scheme to transmit optical frequency signals. The 300 km long fiber link was composed of two 150 km links, and the noise of each link was compensated by a respective phase-locked loop. The two links were connected by a relay station, which included a receiving end, a regenerative amplifier, and a transmitting end. The signal from the upper link was amplified by the regenerative amplifier in the relay station and then transmitted to the lower link by the transmitting end. The regenerative amplifier achieved optical amplification by phase-locking the regenerative laser source to the phase of the transmitted light. This amplification technique had a gain of over 50 dB and a bandwidth of several kHz to several tens of kHz. Its unidirectional nature made it suitable for relay amplification or end-of-link amplification. The cascaded transmission of the phase-controlled segments improved the phase control bandwidth and transmission accuracy of the entire link, and the transmission stability reached 5E-20 / 20 hours.[See Lopez O, Haboucha A, Kéfélian F, Jiang H, Chanteau B, Roncin V, Chardonnet C, Amy-Klein A, Santarelli G. Cascaded multiplexed optical link on a telecommunication network for frequency dissemination. Opt Express. 2010 Aug 2;18(16):16849-57. doi: 10.1364 / OE.18.016849. PMID: 20721077.] In 2012, the French group conducted a 540 km two-stage cascaded optical frequency transmission. The link used six bidirectional EDFA and an optimized relay station optical path structure. The entire transmitted light from the upper link was used for regenerative amplification, and a small part of the regenerated light was returned to the upper level for noise detection. Since the returned light power was much larger than the previous scheme, not only did it improve the signal-to-noise ratio of the in-loop signal of the upper level, but it also expanded the single-stage transmission distance. Finally, they achieved a transmission stability of 3E-19 / 30000s (10 Hz measurement bandwidth).[See Lopez 0, Haboucha A, Chanteau B, Chardonnet C, Amy-Klein A, Santarelli G. Ultra-stable long distance optical frequency distribution using the Internet fiber network. Opt Express. 2012 Oct 8;20(21):23518-26. doi: 10.1364 / OE.20.023518. PMID: 23188314.] In 2015, the French group achieved a total length of 1480km four-stage cascaded optical fiber optical frequency transfer, a total of 3 relay stations and 16 bidirectional EDFA were used in the link, by controlling the phase of each link segment, a transfer stability of 2E-20 / 8000s was achieved. [See Chiodo N, Quintin N, Stefani F, Wiotte F, Camisard E, Chardonnet C, Santarelli G, Amy-Klein A, Pottie PE, Lopez 0. Cascaded optical fiber link using the internet network for remote clocks comparison. Opt Express. 2015 Dec 28;23(26):33927-37. doi: 10.1364 / OE.23.033927. PMID: 26832051.]. SUMMARY

[0004] The purpose of the present application is to provide an alternating optical frequency transfer regenerative repeater system and method without out-of-band noise, which uses an online Faraday rotator to reduce the asymmetry of the transmission structure, and the in-band link does not need temperature control, has the advantages of simple system structure, low overall noise, long transmission distance and repeatability.

[0005] To achieve the above purpose, the technical solution of the present application is as follows:

[0006] An optical frequency transfer structure of regenerative repeater amplification, comprising a local end, a regenerative repeater end, a regenerative repeater end and a user end, characterized in that,

[0007] The local end comprises a first reference frequency source, a first laser, a first Y-type optical coupler, a first online Faraday rotator, a second online Faraday rotator, a second Y-type optical coupler, a first acousto-optic modulator, a third Y-type optical coupler, a first photoelectric detector, a first servo control module, a first direct digital frequency synthesizer, a second acousto-optic modulator, a second photoelectric detector.

[0008] The optical signal to be transmitted is emitted from the first laser, input from a second port of the first Y-type optical coupler, a first port of the first Y-type optical coupler is connected to the first online Faraday rotator, the first online Faraday rotator is connected to the second online Faraday rotator, the second online Faraday rotator is connected to a first port of the second Y-type optical coupler, a second port of the second Y-type optical coupler is connected to the first acousto-optic modulator, the first acousto-optic modulator is connected to the transmission link; a third port of the first Y-type optical coupler is connected to a first port of the third Y-type optical coupler, a second port of the third Y-type optical coupler is connected to the first photoelectric detector, an output of the second photoelectric detector is connected to the first reference frequency source, and the first reference frequency source is connected to the first servo control module, the first servo control module is connected to the first direct digital frequency synthesizer, and the first direct digital frequency synthesizer is connected to a radio frequency port of the first acousto-optic modulator; a third port of the third Y-type optical coupler is connected to the second acousto-optic modulator, and the second acousto-optic modulator is connected to the second photoelectric detector.

[0009] The regenerative repeater end comprises a second reference frequency source, a first polarization controller, a third acousto-optic modulator, a fourth Y-type optical coupler, a third online Faraday rotator, a fifth Y-type optical coupler, a sixth Y-type optical coupler, a third photoelectric detector, a fourth photoelectric detector, a first frequency division module, a second servo control module, a second laser, a seventh Y-type optical coupler, an eighth Y-type optical coupler, a fifth photoelectric detector, a fourth acousto-optic modulator, a ninth Y-type optical coupler, a fourth online Faraday rotator, a fifth online Faraday rotator, a tenth Y-type optical coupler, a fifth acousto-optic modulator, a sixth photoelectric detector, a first frequency mixer, a third servo control module, a second direct digital frequency synthesizer, a seventh photoelectric detector.

[0010] The first acousto-optic modulator of the local end is connected with the first polarization controller of the regenerative repeater through an optical fiber link, the first polarization controller is connected with the second port of the fourth Y-type optical coupler, the third port of the fourth Y-type optical coupler is connected with the third acousto-optic modulator; the first port of the fourth Y-type optical coupler is connected with the third in-line Faraday rotator, the first port of the fifth Y-type optical coupler is connected with the third in-line Faraday rotator, the first port of the sixth Y-type optical coupler is connected with the third port of the fifth Y-type optical coupler, and the third port of the sixth Y-type optical coupler is connected with the third photoelectric detector; the second port of the sixth Y-type optical coupler is connected with the fourth photoelectric detector, the fourth photoelectric detector is connected with the first frequency division module, the output of the first frequency division module is input to the second servo control module together with the second reference frequency source, and the output of the second servo control module is used for locking the second laser; the second laser is connected with the third port of the seventh Y-type optical coupler, the first port of the seventh Y-type optical coupler is connected with the first port of the eighth Y-type optical coupler, the second port of the eighth Y-type optical coupler is connected with the second port of the fifth Y-type optical coupler; the third port of the eighth Y-type optical coupler is connected with the fourth acousto-optic modulator, the second port of the ninth Y-type optical coupler is connected with the fourth acousto-optic modulator, the first port of the Y-type optical coupler is connected with the fourth in-line Faraday rotator, the fourth in-line Faraday rotator is connected with the fifth in-line Faraday rotator, the first port of the tenth Y-type optical coupler is connected with the fifth in-line Faraday rotator, and the third port of the tenth Y-type optical coupler is connected with the seventh photoelectric detector; the second port of the seventh Y-type optical coupler is connected with the fifth photoelectric detector; the third port of the ninth Y-type optical coupler is connected with the sixth photoelectric detector; the output ends of the fifth photoelectric detector and the sixth photoelectric detector are connected to the input end of the first frequency mixer, the output of the first frequency mixer is input to the third servo control module together with the second reference frequency source, the third servo control module is connected with the second direct digital frequency synthesizer, and the second direct digital frequency synthesizer is connected to the radio frequency port of the fifth acousto-optic modulator.

[0011] The regenerative relay end comprises a third reference frequency source, a second polarization controller, an eleventh Y-type optical coupler, a sixth acousto-optic modulator, a sixth online Faraday rotator, a twelfth Y-type optical coupler, a thirteenth Y-type optical coupler, an eighth photodetector, a ninth photodetector, a second frequency division module, a fourth servo control module, a third laser, a fourteenth Y-type optical coupler, a fifteenth Y-type optical coupler, a tenth photodetector, a seventh acousto-optic modulator, a sixteenth Y-type optical coupler, a seventh online Faraday rotator, an eighth online Faraday rotator, a seventeenth Y-type optical coupler, an eighth acousto-optic modulator, an eleventh photodetector, a second frequency mixer, a fifth servo control module, a third direct digital frequency synthesizer, a twelfth photodetector.

[0012] The fifth acousto-optic modulator of the regenerative repeater is connected to the second polarization controller of the regenerative repeater through an optical fiber link, the second polarization controller is connected to the second port of the eleventh Y-type optical coupler, the third port of the eleventh Y-type optical coupler is connected to the sixth acousto-optic modulator; the first port of the eleventh Y-type optical coupler is connected to the sixth in-line Faraday rotator, the sixth in-line Faraday rotator is connected to the first port of the twelfth Y-type optical coupler, the third port of the twelfth Y-type optical coupler is connected to the first port of the thirteenth Y-type optical coupler, the second port of the thirteenth Y-type optical coupler is connected to the eighth photodetector; the third port of the thirteenth Y-type optical coupler is connected to the ninth photodetector, the ninth photodetector is connected to the second frequency division module, the output of the second frequency division module and the third reference frequency source are commonly input to the fourth servo control module, the output of the fourth servo control module is used for locking the third laser; the third laser is connected to the second port of the fourteenth Y-type optical coupler, the first port of the fourteenth Y-type optical coupler is connected to the first port of the fifteenth Y-type optical coupler, the second port of the fifteenth Y-type optical coupler is connected to the second port of the twelfth Y-type optical coupler; the third port of the fifteenth Y-type optical coupler is connected to the seventh acousto-optic modulator, the seventh acousto-optic modulator is connected to the second port of the sixteenth Y-type optical coupler, the first port of the sixteenth Y-type optical coupler is connected to the seventh in-line Faraday rotator, the seventh in-line Faraday rotator is connected to the eighth in-line Faraday rotator, the eighth in-line Faraday rotator is connected to the first port of the seventeenth Y-type optical coupler, the third port of the seventeenth Y-type optical coupler is connected to the twelfth photodetector; the third port of the fourteenth Y-type optical coupler is connected to the tenth photodetector; the third port of the sixteenth Y-type optical coupler is connected to the eleventh photodetector; the output of the tenth photodetector and the eleventh photodetector are connected to the input of the second frequency mixer, the output of the second frequency mixer and the third reference frequency source are commonly input to the fifth servo control module, the fifth servo control module is connected to the third direct digital frequency synthesizer, the third direct digital frequency synthesizer is connected to the radio frequency port of the eighth acousto-optic modulator.

[0013] The user terminal comprises a fourth reference frequency source, a third polarization controller, an eighteenth Y-type optical coupler, a ninth acousto-optic modulator, a ninth in-line Faraday rotator, a nineteenth Y-type optical coupler, a twentieth Y-type optical coupler, a thirteenth photodetector, a fourteenth photodetector, a third frequency division module, a sixth servo control module, a fourth laser, a twenty-first Y-type optical coupler.

[0014] The eighth acousto-optic modulator of the regenerative relay end is connected with the third polarization controller of the user end through an optical fiber link, the third polarization controller is connected with the second port of the eighteenth Y-type optical coupler, and the third port of the eighteenth Y-type optical coupler is connected with the ninth acousto-optic modulator; the first port of the eighteenth Y-type optical coupler is connected with the ninth in-line Faraday rotator, the ninth in-line Faraday rotator is connected with the first port of the nineteenth Y-type optical coupler, the third port of the nineteenth Y-type optical coupler is connected with the first port of the twentieth Y-type optical coupler, and the third port of the twentieth Y-type optical coupler is connected with the thirteenth photodetector; the second port of the twentieth Y-type optical coupler is connected with the fourteenth photodetector, the fourteenth photodetector is connected with the third frequency division module, the output of the third frequency division module is output to the sixth servo control module together with the fourth reference frequency source, and the output of the sixth servo control module is used for locking the fourth laser; the fourth laser is connected with the first port of the twenty-first Y-type optical coupler, the third port of the twenty-first Y-type optical coupler is connected with the second port of the nineteenth Y-type optical coupler, and the signal transmitted by the second port of the twenty-first Y-type optical coupler is the received signal.

[0015] The optical frequency transfer method of the system comprises the following steps:

[0016] The local end:

[0017] The optical signal to be transferred is E0, wherein, ω0 and are the angular frequency and initial phase of the optical signal to be transferred.

[0018] After input through the second port of the first Y-type coupler, the signal is output to the first in-line Faraday rotator through the first port; the signal is divided into two paths through the first in-line Faraday rotator, one path of the reflected light signal is input through the first port and output through the third port of the first Y-type optical coupler, and then reaches the first photodetector through the third Y-type optical coupler, and the signal is still recorded as E0; the other path of the transmitted light signal is sequentially input into the optical fiber link through the second in-line Faraday rotator, the second Y-type optical coupler and the first acousto-optic modulator, and the signal is recorded as E1, and the expression is

[0019]

[0020] In the formula, ω1 and are the frequency and initial phase of the radio frequency operation of the first acousto-optic modulator, is the phase noise introduced by the optical fiber link;

[0021] The signal E1 is received by the fourth photoelectric detector after passing through the first polarization controller, the fourth Y-type optical coupler, the third online Faraday rotator, the fifth Y-type optical coupler and the sixth Y-type optical coupler in sequence.

[0022] The light signal E2 emitted by the second laser, where ω2 and are the frequency and initial phase of the second laser,

[0023] The light signal E2 passes through the seventh Y-type optical coupler, the eighth Y-type optical coupler and the fifth Y-type optical coupler, is reflected at the third online Faraday rotator, passes through the fifth Y-type optical coupler and the sixth Y-type optical coupler, reaches the fourth photoelectric detector to beat with the signal E1, and the beat signal is frequency-divided at the first frequency division module and input to the second servo control module together with the reference signal of the second reference frequency source to be locked to -ω N , and the output direct current error signal V e，0 , The second laser is feedback controlled.

[0024] When the second servo control module works in the locked state, V e，0 is close to 0, that is:

[0025]

[0026] ω2 = ω0 + ω1 - ω N

[0027] The light signal output by the locked second laser The signal after passing through the seventh Y-type optical coupler, the eighth Y-type optical coupler, the fifth Y-type optical coupler, the third online Faraday rotator, the fourth Y-type optical coupler, the first polarization controller, the fiber link and the first acousto-optic modulator is recorded as E3, and the expression of the signal is

[0028]

[0029] The signal E3 passes through the second Y-type optical coupler, the second online Faraday rotator, the first online Faraday rotator, the first Y-type Y-type optical coupler and the third Y-type optical coupler, reaches the first photoelectric detector to beat with the signal E0, and the beat signal is input to the first servo control module for locking, and the output direct current error signal V e，1 enters the servo control module, and the expression is:

[0030]

[0031] When the first servo control module works in the locked state, V e，1Approaching 0, the expression can be further written as:

[0032]

[0033] The signal after locking is compensated to the first acousto-optic modulator, which can compensate the phase noise introduced by the optical fiber link;

[0034] The first regenerative relay end:

[0035] After transmission through the transmission link, the received signal E4 is represented as:

[0036] The signal E4 passes through the first polarization controller, the fourth Y-type optical coupler, the third online Faraday rotator, the fifth Y-type optical coupler, the sixth Y-type optical coupler, and reaches the fourth photodetector;

[0037] The light signal E2 emitted by the second laser passes through the seventh Y-type optical coupler, the eighth Y-type optical coupler and the fifth Y-type optical coupler, is reflected at the third online Faraday rotator, passes through the fifth Y-type optical coupler and the sixth Y-type optical coupler, reaches the fourth photodetector and beats with the signal E4, and the beat signal is input to the second servo control module together with the reference signal of the second reference frequency source after frequency division at the first frequency division module, and is locked to -ω N , the output DC error signal V e，2 into the servo control module, and its expression is:

[0038]

[0039] When the second servo control module works in the locking state, V e，z Approaching 0, the expression can be further written as:

[0040]

[0041] ω2=ω0+ω1-ω N

[0042] The locked light signal is After passing through the seventh Y-type optical coupler (35), the optical signal is divided into two paths. One path of the optical signal passes through the fifth Y-type optical coupler, is reflected at the third online Faraday rotator, passes through the fifth Y-type optical coupler, the eighth Y-type optical coupler and the seventh Y-type optical coupler, and reaches the fifth photodetector. The signal expression is still E2. The other path of the optical signal passes through the fourth acousto-optic modulator and the ninth Y-type optical coupler. The signal is divided into two paths at the fourth online Faraday rotator. One path of the optical signal is reflected, passes through the ninth Y-type optical coupler, and the optical signal is again divided into two paths. One path of the optical signal after passing through the fourth acousto-optic modulator, the eighth Y-type optical coupler and the seventh Y-type optical coupler is denoted as E5. The signal E5 reaches the fifth photodetector and beats with the signal E2. The beat signal is transmitted to the first frequency mixer. The beat signal is denoted as E6. The other path of the optical signal reaches the sixth photodetector and is denoted as E7. The signal expression is

[0043]

[0044]

[0045]

[0046] In the formula, ω1 is the frequency at which the fourth acousto-optic modulator operates at radio frequency, and the frequency shift direction of the first acousto-optic modulator is consistent, is the phase noise introduced by the second reference frequency source;

[0047] The other path of the optical signal at the fourth online Faraday rotator passes through the fourth online Faraday rotator, the fifth online Faraday rotator, the tenth Y-type optical coupler, the fifth acousto-optic modulator and the optical fiber link. The signal expression is denoted as E8. The signal expression is

[0048]

[0049] In the formula, ω1 and is the frequency at which the fifth acousto-optic modulator operates at radio frequency and the initial phase, and the frequency shift direction of the first acousto-optic modulator is opposite, is the phase noise introduced by the optical fiber link;

[0050] The signal E8 passes through the second polarization controller, the eleventh Y-type optical coupler, the sixth online Faraday rotator, the twelfth Y-type optical coupler, the thirteenth Y-type optical coupler, and reaches the ninth photodetector.

[0051] The optical signal emitted by the third laser is In the formula, ω3 and is the frequency and initial phase of the third laser, signal E9 passes through the fourteenth Y-type optical coupler, the fifteenth Y-type optical coupler, the twelfth Y-type optical coupler, is reflected at the sixth online Faraday rotator, passes through the twelfth Y-type optical coupler and the thirteenth Y-type optical coupler, reaches the ninth photodetector to beat with signal E8, the beat signal passes through the second frequency division module after frequency division, and a reference signal of the third reference frequency source is input into the fourth servo control module together to be locked to ω N , the output direct current error signal V e，3 enters the servo control module, and its expression is:

[0052]

[0053] When the fourth servo control module works in the locked state, V e，3 is close to 0, and the expression can be further written as:

[0054]

[0055] ω3 = ω0 + ω1

[0056] The locked optical signal is Signal E 10 after the fourteenth Y-type optical coupler, the fifteenth Y-type optical coupler, the twelfth Y-type optical coupler, the sixth online Faraday rotator, the eleventh Y-type optical coupler, the second polarization controller, the optical fiber link and the fifth acousto-optic modulator is recorded as E

[0057]

[0058] Signal E 10 passes through the tenth Y-type optical coupler, the fifth online Faraday rotator, the fourth online Faraday rotator and the ninth Y-type optical coupler, beats with signal E7 at the sixth photodetector, and the beat signal is recorded as E 11 , signal E 11 transmits to the first frequency mixer to mix with signal E6, and the mixed signal is recorded as E 12 , and the expression of the signal is

[0059]

[0060]

[0061] Mixed signal E 12 and a reference signal of the second reference frequency source are input into the third servo control module together to be locked, and the output direct current error signal V e，4 enters the servo control module, and its expression is:

[0062]

[0063] When the third servo control module works in the locking state, V e，4 is close to 0, the expression can be further written as:

[0064]

[0065] The locked signal is compensated to the fifth acousto-optic modulator, so as to compensate the phase noise introduced by the reference frequency source and the optical fiber link of the regenerative repeater.

[0066] The second regenerative repeater:

[0067] In the regenerative repeater, after transmission through the transmission link, the received signal can be expressed as:

[0068]

[0069] The signal E 13 passes through the second polarization controller, the eleventh Y-type optical coupler, the sixth online Faraday rotator, the twelfth Y-type optical coupler, the thirteenth Y-type optical coupler, and reaches the ninth photodetector.

[0070] The optical signal emitted by the third laser is The signal E9 passes through the fourteenth Y-type optical coupler, the fifteenth Y-type optical coupler, the twelfth Y-type optical coupler, is reflected at the sixth online Faraday rotator, passes through the twelfth Y-type optical coupler and the thirteenth Y-type optical coupler, and reaches the ninth photodetector to be combined with the signal E 13 The beat frequency, after the beat frequency signal is frequency-divided at the second frequency division module, is input to the fourth servo control module together with the reference signal of the third reference frequency source to be locked to ω N , the output direct current error signal V e，5 enters the servo control module, and the expression is:

[0071]

[0072] When the fourth servo control module works in the locking state, V e，5 is close to 0, the expression can be further written as:

[0073]

[0074] ω3=ω0+ω1

[0075] The locked optical signal is After passing through the fourteenth Y-type optical coupler, the optical signal is split into two paths at the fifteenth Y-type optical coupler. One path passes through the twelfth Y-type optical coupler, is reflected at the sixth in-line Faraday rotator, and then passes through the twelfth, fifteenth, and fourteenth Y-type optical couplers before reaching the tenth photodetector. The other path passes through the seventh acousto-optic modulator and the sixteenth Y-type optical coupler. At the seventh in-line Faraday rotator, the signal is split into two paths. One path is reflected, and after passing through the sixteenth Y-type optical coupler, it is split into two paths again. The signal expression of the other path after passing through the seventh acousto-optic modulator, the fifteenth Y-type optical coupler, and the fourteenth Y-type optical coupler is denoted as E. 14 The signal reaches the tenth photodetector and beats with signal E9. The beat signal is transmitted to the second mixer and is denoted as E. 15 Another optical signal arrives at the eleventh photodetector, denoted as E. 16 The signal expression is as follows:

[0076]

[0077]

[0078]

[0079] In the formula, ω1 is the frequency at which the seventh acousto-optic modulator (65) operates at radio frequency, but it is opposite to the frequency shift direction of the first acousto-optic modulator. It is phase noise introduced by the third reference frequency source.

[0080] The other optical signal at the seventh online Faraday rotator passes through the seventh online Faraday rotator, the eighth online Faraday rotator, the seventeenth Y-type optical coupler, the eighth acousto-optic modulator, and the optical fiber link. The signal expression is denoted as E. 17 The signal expression is as follows:

[0081]

[0082] In the formula, ω1 is the frequency at which the eighth acousto-optic modulator operates at radio frequency, which is consistent with the frequency shift direction of the first acousto-optic modulator. It is the initial phase of the eighth acousto-optic modulator. This is phase noise introduced by the fiber optic link. The signal E mentioned above... 17 After passing through the third polarization controller, the eighteenth Y-type optical coupler, the ninth online Faraday rotator, the nineteenth Y-type optical coupler, and the twentieth Y-type optical coupler, it reaches the fourteenth photodetector.

[0083] The light signal emitted by the fourth laser is In the formula, ω4 and is the frequency and initial phase of the fourth laser, signal E 18 through the twenty-first Y-type optical coupler, the nineteenth Y-type optical coupler, reflected at the ninth inline Faraday rotator, through the nineteenth Y-type optical coupler, the twentieth Y-type optical coupler, to the fourteenth photodetector, and signal E 17 beat frequency, the beat frequency signal is input to the sixth servo control module together with the reference signal of the fourth reference frequency source after frequency division at the third frequency division module, and is locked to -ω N , the output direct current error signal V e，6 into the servo control module, and its expression is:

[0084]

[0085] when the sixth servo control module works in the locked state, V e，6 is close to 0, and the expression can be further written as:

[0086]

[0087] ω4=ω0+ω1-ω N

[0088] the locked optical signal is the signal after the twenty-first Y-type optical coupler, the nineteenth Y-type optical coupler, the ninth inline Faraday rotator, the eighteenth Y-type optical coupler, the third polarization controller, the optical fiber link, and the eighth acousto-optic modulator is recorded as E 19 , and the signal expression is

[0089]

[0090] the signal E 19 through the seventeenth Y-type optical coupler, the eighth inline Faraday rotator, the seventh inline Faraday rotator, the sixteenth Y-type optical coupler, at the eleventh photodetector, and signal E 16 beat frequency, the beat frequency signal is recorded as E 20 , signal E 20 transmitted to the first mixer and signal E 15 mixing, the mixing signal is recorded as E 21 , and the signal expression is:

[0091]

[0092]

[0093] mixing signal E 21 is input to the fifth servo control module together with the reference signal of the third reference frequency source for locking, and the output direct current error signal V e，7The expression of the entering servo control module is:

[0094]

[0095] When the fifth servo control module works in the locking state, V e，7 is close to 0, and the expression can be further written as:

[0096]

[0097] The signal after locking is compensated to the eighth acousto-optic modulator, so as to compensate the phase noise introduced by the reference frequency source of the regenerative repeater end (3) and the optical fiber link;

[0098] The user end:

[0099] In the user end, the received signal E 22 is expressed as:

[0100]

[0101] The signal E 22 passes through a third polarization controller, an eighteenth Y-type optical coupler, a ninth online Faraday rotator, a nineteenth Y-type optical coupler, a twentieth Y-type optical coupler, and reaches a fourteenth photodetector;

[0102] The optical signal emitted by the fourth laser is passes through a twenty-first Y-type optical coupler, a nineteenth Y-type optical coupler, is reflected at the ninth online Faraday rotator, passes through the nineteenth Y-type optical coupler, the twentieth Y-type optical coupler, and reaches the fourteenth photodetector to be combined with the signal E 22 The beat frequency, after the beat frequency signal is frequency-divided at the third frequency division module, is input to the sixth servo control module together with the reference signal of the fourth reference frequency source to be locked to -ω N , and a direct current error signal V e，8 enters the servo control module, and the expression is:

[0103]

[0104] When the sixth servo control module works in the locking state, V e，8 is close to 0, and the expression can be further written as:

[0105]

[0106] ω4=ω0+ω1-ω N

[0107] The locked optical signal is Compensate the phase noise introduced by the reference frequency source and the fiber link in each station, so that the phase stable optical frequency signal is obtained at the user end.

[0108] Compared with the prior art, the present application has the beneficial effects that:

[0109] 1) The present application uses an online Faraday rotator to reduce the asymmetry of the transmission structure, greatly reducing the influence of out-of-band noise on the stability of the system.

[0110] 2) The present application does not require a complex temperature control system, greatly simplifying the requirements of the control circuit.

[0111] 3) The structure of the present application is repeatable, and by alternately arranging regenerative relay stations, the optical frequency signal to be transmitted can be regenerated and amplified while suppressing the phase noise introduced by the transmission link.

[0112] 4) By alternately cascading the regenerative relay of the present application, it can be applied to a super-long distance phase-stable optical frequency transmission system. BRIEF DESCRIPTION OF DRAWINGS

[0113] Figure 1 It is a local end structure diagram of the regenerative relay optical frequency transmission system of the present application.

[0114] Figure 2 It is a first regenerative relay end structure diagram of the regenerative relay optical frequency transmission system of the present application.

[0115] Figure 3 It is a second regenerative relay end structure diagram of the regenerative relay optical frequency transmission system of the present application.

[0116] Figure 4 It is a user end structure diagram of the regenerative relay optical frequency transmission system of the present application.

[0117] Figure 5 It is a structure cascade diagram of the regenerative relay optical frequency transmission system of the present application. DETAILED DESCRIPTION

[0118] The present application will be further described below in conjunction with the embodiments and drawings, the present embodiments are implemented on the basis of the technical solutions of the present application, detailed implementation methods and specific work processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0119] Example 1

[0120] First, see Figures 1 to 4 , Figures 1 to 4The structure schematic view of the embodiment of the regenerative relay optical frequency transfer system of the present application, from the figure, the regenerative relay optical frequency transfer system of the present application comprises a local end 1, a regenerative relay end 2, a regenerative relay end 3 and a user end 4;

[0121] The local end 1 comprises a first reference frequency source 5, a first laser 11, a first Y-type optical coupler 12, a first online Faraday rotator 13, a second online Faraday rotator 14, a second Y-type optical coupler 15, a first acousto-optic modulator 16, a third Y-type optical coupler 17, a first photoelectric detector 18, a first servo control module 19, a first direct digital frequency synthesizer 20, a second acousto-optic modulator 21 and a second photoelectric detector 22.

[0122] The optical signal to be transferred is emitted from the first laser 11 and input from the second port of the first Y-type optical coupler 12, the first port of the first Y-type optical coupler 12 being connected to the first online Faraday rotator 13, the first online Faraday rotator 13 being connected to the second online Faraday rotator 14, the second online Faraday rotator 14 being connected to the first port of the second Y-type optical coupler 15, the second port of the second Y-type optical coupler 15 being connected to the first acousto-optic modulator 16, the first acousto-optic modulator 16 being connected to the transmission link 2; the third port of the first Y-type optical coupler 12 is connected to the first port of the third Y-type optical coupler 17, the second port of the third Y-type optical coupler 17 being connected to the first photoelectric detector 18, the output of the second photoelectric detector 18 being connected to the first reference frequency source 5 and being input to the first servo control module 19 together, the first servo control module 19 being connected to the first direct digital frequency synthesizer 20, the first direct digital frequency synthesizer 20 being connected to the radio frequency port of the first acousto-optic modulator 16; the third port of the third Y-type optical coupler 17 is connected to the second acousto-optic modulator 21, and the second acousto-optic modulator 21 is connected to the second photoelectric detector 22.

[0123] The regenerative repeater 2 comprises a second reference frequency source 6, a first polarization controller 23, a third acousto-optic modulator 24, a fourth Y-type optical coupler 25, a third on-line Faraday rotator 26, a fifth Y-type optical coupler 27, a sixth Y-type optical coupler 28, a third photodetector 29, a fourth photodetector 30, a first frequency division module 31, a second servo control module 33, a second laser 34, a seventh Y-type optical coupler 35, an eighth Y-type optical coupler 36, a fifth photodetector 37, a fourth acousto-optic modulator 38, a ninth Y-type optical coupler 39, a fourth on-line Faraday rotator 40, a fifth on-line Faraday rotator 41, a tenth Y-type optical coupler 42, a fifth acousto-optic modulator 43, a sixth photodetector 44, a first frequency mixer 45, a third servo control module 47, a second direct digital frequency synthesizer 48, a seventh photodetector 49.

[0124] The first acousto-optic modulator 16 of the local end 1 is connected to the first polarization controller 23 of the regenerative repeater end 2 through an optical fiber link, the first polarization controller 23 is connected to the second port of the fourth Y-type optical coupler 25, the third port of the fourth Y-type optical coupler 25 is connected to the third acousto-optic modulator 24; the first port of the fourth Y-type optical coupler 25 is connected to the third in-line Faraday rotator 26, the third in-line Faraday rotator 26 is connected to the first port of the fifth Y-type optical coupler 27, the third port of the fifth Y-type optical coupler 27 is connected to the first port of the sixth Y-type optical coupler 28, the third port of the sixth Y-type optical coupler 28 is connected to the third photoelectric detector 29; the second port of the sixth Y-type optical coupler 28 is connected to the fourth photoelectric detector 30, the fourth photoelectric detector 30 is connected to the first frequency division module 31, the output of the first frequency division module 31 is input to the second servo control module 33 together with the second reference frequency source 6, the output of the second servo control module 33 is used to lock the second laser 34; the second laser 34 is connected to the third port of the seventh Y-type optical coupler 35, the first port of the seventh Y-type optical coupler 35 is connected to the first port of the eighth Y-type optical coupler 36, the second port of the eighth Y-type optical coupler 36 is connected to the second port of the fifth Y-type optical coupler 27; the third port of the eighth Y-type optical coupler 36 is connected to the fourth acousto-optic modulator 38, the fourth acousto-optic modulator 38 is connected to the second port of the ninth Y-type optical coupler 39, the first port of the Y-type optical coupler 39 is connected to the fourth in-line Faraday rotator 40, the fourth in-line Faraday rotator 40 is connected to the fifth in-line Faraday rotator 41, the fifth in-line Faraday rotator 41 is connected to the first port of the tenth Y-type optical coupler 42, the third port of the tenth Y-type optical coupler 42 is connected to the seventh photoelectric detector 49; the second port of the seventh Y-type optical coupler 35 is connected to the fifth photoelectric detector 37; the third port of the ninth Y-type optical coupler 39 is connected to the sixth photoelectric detector 44; the outputs of the fifth photoelectric detector 37 and the sixth photoelectric detector 44 are connected to the inputs of the first frequency mixer 45, the output of the first frequency mixer 45 is input to the third servo control module 47 together with the second reference frequency source 6, the third servo control module 47 is connected to the second direct digital frequency synthesizer 48, the second direct digital frequency synthesizer 48 is connected to the radio frequency port of the fifth acousto-optic modulator 43.

[0125] The regenerative relay end 3 comprises a third reference frequency source 7, a second polarization controller 50, an eleventh Y-type optical coupler 51, a sixth acousto-optic modulator 52, a sixth inline Faraday rotator 53, a twelfth Y-type optical coupler 54, a thirteenth Y-type optical coupler 55, an eighth photodetector 56, a ninth photodetector 57, a second frequency division module 58, a fourth servo control module 60, a third laser 61, a fourteenth Y-type optical coupler 62, a fifteenth Y-type optical coupler 63, a tenth photodetector 64, a seventh acousto-optic modulator 65, a sixteenth Y-type optical coupler 66, a seventh inline Faraday rotator 67, an eighth inline Faraday rotator 68, a seventeenth Y-type optical coupler 69, an eighth acousto-optic modulator 70, an eleventh photodetector 71, a second frequency mixer 72, a fifth servo control module 74, a third direct digital frequency synthesizer 75, a twelfth photodetector 76.

[0126] The fifth acousto-optic modulator 43 of the regenerative repeater end 2 is connected with the second polarization controller 50 of the regenerative repeater end 3 through an optical fiber link, the second polarization controller 50 is connected with the second port of the eleventh Y-type optical coupler 51, the third port of the eleventh Y-type optical coupler 51 is connected with the sixth acousto-optic modulator 52; the first port of the eleventh Y-type optical coupler 51 is connected with the sixth in-line Faraday rotator 53, the sixth in-line Faraday rotator 53 is connected with the first port of the twelfth Y-type optical coupler 54, the third port of the twelfth Y-type optical coupler 54 is connected with the first port of the thirteenth Y-type optical coupler 55, the second port of the thirteenth Y-type optical coupler 55 is connected with the eighth photodetector 56; the third port of the thirteenth Y-type optical coupler 55 is connected with the ninth photodetector 57, the ninth photodetector 57 is connected with the second frequency division module 58, the output of the second frequency division module 58 is commonly input to the fourth servo control module 60 together with the third reference frequency source 7, the output of the fourth servo control module 60 is used for locking the third laser 61; the third laser 61 is connected with the second port of the fourteenth Y-type optical coupler 62, the first port of the fourteenth Y-type optical coupler 62 is connected with the first port of the fifteenth Y-type optical coupler 63, the second port of the fifteenth Y-type optical coupler 63 is connected with the second port of the twelfth Y-type optical coupler 54; the third port of the fifteenth Y-type optical coupler 63 is connected with the seventh acousto-optic modulator 65, the seventh acousto-optic modulator 65 is connected with the second port of the sixteenth Y-type optical coupler 66, the first port of the sixteenth Y-type optical coupler 66 is connected with the seventh in-line Faraday rotator 67, the seventh in-line Faraday rotator 67 is connected with the eighth in-line Faraday rotator 68, the eighth in-line Faraday rotator 68 is connected with the first port of the seventeenth Y-type optical coupler 69, the third port of the seventeenth Y-type optical coupler 69 is connected with the twelfth photodetector 76; the third port of the fourteenth Y-type optical coupler 62 is connected with the tenth photodetector 64; the third port of the sixteenth Y-type optical coupler 66 is connected with the eleventh photodetector 71; the output ends of the tenth photodetector 64 and the eleventh photodetector 71 are connected to the input end of the second frequency mixer 72, the output of the second frequency mixer 72 is commonly input to the fifth servo control module 74 together with the third reference frequency source 7, the fifth servo control module 74 is connected with the third direct digital frequency synthesizer 75, the third direct digital frequency synthesizer 75 is connected to the radio frequency port of the eighth acousto-optic modulator 70.

[0127] The user terminal 4 includes a fourth reference frequency source 8, a third polarization controller 77, an eighteenth Y-type optical coupler 78, a ninth acousto-optic modulator 79, a ninth inline Faraday rotator 80, a nineteenth Y-type optical coupler 81, a twentieth Y-type optical coupler 82, a thirteenth photodetector 83, a fourteenth photodetector 84, a third frequency division module 85, a sixth servo control module 87, a fourth laser 88, a twenty-first Y-type optical coupler 89.

[0128] The eighth acousto-optic modulator 70 of the regenerative repeater 3 is connected to the third polarization controller 77 of the user terminal 4 through an optical fiber link, the third polarization controller 77 is connected to the second port of the eighteenth Y-type optical coupler 78, the third port of the eighteenth Y-type optical coupler 78 is connected to the ninth acousto-optic modulator 79; the first port of the eighteenth Y-type optical coupler 78 is connected to the ninth inline Faraday rotator 80, the ninth inline Faraday rotator 80 is connected to the first port of the nineteenth Y-type optical coupler 81, the third port of the nineteenth Y-type optical coupler 81 is connected to the first port of the twentieth Y-type optical coupler 82, the third port of the twentieth Y-type optical coupler 82 is connected to the thirteenth photodetector 83; the second port of the twentieth Y-type optical coupler 82 is connected to the fourteenth photodetector 84, the fourteenth photodetector 84 is connected to the third frequency division module 85, the output of the third frequency division module 85 is connected to the fourth reference frequency source 8, and the output of the fourth reference frequency source 8 is connected to the sixth servo control module 87, and the output of the sixth servo control module 87 is used to lock the fourth laser 88; the fourth laser 88 is connected to the first port of the twenty-first Y-type optical coupler 89, the third port of the twenty-first Y-type optical coupler 89 is connected to the second port of the nineteenth Y-type optical coupler 81, and the signal transmitted by the second port of the twenty-first Y-type optical coupler 89 is the received signal.

[0129] The optical frequency transfer method of the above system includes the following steps:

[0130] The local terminal:

[0131] The optical signal to be transferred is After passing through the first Y-type optical coupler 12 and the first inline Faraday rotator 13, the optical signal is divided into two paths, one path of the optical signal is reflected back through the first Y-type optical coupler 12 and the third Y-type optical coupler 17 to the first photodetector 18, and the signal expression is still E0, and the other path passes through the second inline Faraday rotator 14, the second Y-type optical coupler 15, the first acousto-optic modulator 16 and the optical fiber link, and the signal after the optical fiber link is denoted as E1, and the signal expression is

[0132]

[0133] where 38MHz and is the frequency and initial phase of the RF operation of the first acousto-optic modulator 16, is the phase noise introduced by the fiber link. The signal El is passed through the first polarization controller 23, the fourth Y-coupler 25, the third in-line Faraday rotator 26, the fifth Y-coupler 27, the sixth Y-coupler 28, and reaches the fourth photodetector 30.

[0134] The optical signal emitted by the second laser 34 is where v1and is the frequency and initial phase of the second laser 34, the signal E2 is passed through the seventh Y-coupler 35, the eighth Y-coupler 36, and the fifth Y-coupler 27, reflected at the third in-line Faraday rotator 26, passed through the fifth Y-coupler 27, the sixth Y-coupler 28, and reaches the fourth photodetector 30 to beat with the signal El, the beat signal is passed through the first frequency division module 31 and the reference signal of the second reference frequency source 6 is input into the second servo control module 33 to be locked, the output direct current error signal V e，0 into the servo control module, the expression is:

[0135]

[0136] When the second servo control module works in the locked state, V e，0 is close to 0, the expression can be further written as:

[0137]

[0138] v1= v0- 108MHz

[0139] The locked optical signal is The signal after passing through the seventh Y-coupler 35, the eighth Y-coupler 36, the fifth Y-coupler 27, the third in-line Faraday rotator 26, the fourth Y-coupler 25, the first polarization controller 23, the fiber link, and the first acousto-optic modulator 16 is recorded as E3, the expression of the signal is

[0140]

[0141] The signal E3 is passed through the second Y-coupler 15, the second in-line Faraday rotator 14, the first in-line Faraday rotator 13, the first Y-coupler 12, and the third Y-coupler 17, and reaches the first photodetector 18 to beat with the signal E0, the beat signal is input into the first servo control module 19 to be locked, and the output direct current error signal V e，1The expression of the entering servo control module is:

[0142]

[0143] When the first servo control module works in the locking state, V e，1 is close to 0, and the expression can be further written as:

[0144]

[0145] The signal after the locking is compensated to the first acousto-optic modulator 16, so as to compensate the phase noise introduced by the optical fiber link.

[0146] The regenerative repeater (2) comprises:

[0147] In the regenerative repeater 2, the received signal after the transmission through the transmission link can be expressed as:

[0148]

[0149] The signal E4 passes through the first polarization controller 23, the fourth Y-type optical coupler 25, the third online Faraday rotator 26, the fifth Y-type optical coupler 27, the sixth Y-type optical coupler 28, and reaches the fourth photodetector 30.

[0150] The optical signal emitted by the second laser 34 is The signal e2 passes through the seventh Y-type optical coupler 35, the eighth Y-type optical coupler 36 and the fifth Y-type optical coupler 27, is reflected at the third online Faraday rotator 26, passes through the fifth Y-type optical coupler 27 and the sixth Y-type optical coupler 28, reaches the fourth photodetector 30 to beat with the signal E4, and the beat signal is input to the second servo control module 33 after being divided in the first frequency division module 31 and the reference signal of the second reference frequency source 6, and a direct current error signal V e，2 The expression of the entering servo control module is:

[0151]

[0152] When the second servo control module works in the locking state, V e，2 is close to 0, and the expression can be further written as:

[0153]

[0154] v1=v0-108MHz

[0155] The locked optical signal is The light signal is split into two at the eighth Y-type optical coupler 36 through the seventh Y-type optical coupler 35, one of the light signals is reflected at the third inline Faraday rotator 26 through the fifth Y-type optical coupler 27, the eighth Y-type optical coupler 36 and the seventh Y-type optical coupler 35 to the fifth photodetector 37, and the signal expression is still E2; the other light signal is reflected at the fourth inline Faraday rotator 40 through the fourth acousto-optic modulator 38 and the ninth Y-type optical coupler 39, the light signal is split into two again at the ninth Y-type optical coupler 39, one of the light signals is reflected through the fourth acousto-optic modulator 38, the eighth Y-type optical coupler 36 and the seventh Y-type optical coupler 35, and the signal expression is E5, the signal E5 reaches the fifth photodetector 37 to beat with the signal E2, the beat signal is transmitted to the first mixer 45, and the beat signal is E6; the other light signal reaches the sixth photodetector 44, and the signal expression is E7.

[0156]

[0157]

[0158]

[0159] wherein, is the phase noise introduced by the second reference frequency source 6.

[0160] The other light signal at the fourth inline Faraday rotator 40 is transmitted through the fourth inline Faraday rotator 40, the fifth inline Faraday rotator 41, the tenth Y-type optical coupler 42, the fifth acousto-optic modulator 43 and the optical fiber link, and the signal expression is E8, and the signal expression is

[0161]

[0162] wherein, is the initial phase of the fifth acousto-optic modulator 43, is the phase noise introduced by the optical fiber link. The signal E8 is transmitted through the second polarization controller 50, the eleventh Y-type optical coupler 51, the sixth inline Faraday rotator 53, the twelfth Y-type optical coupler 54, the thirteenth Y-type optical coupler 55 to the ninth photodetector 57.

[0163] The light signal emitted by the third laser 61 is wherein, v2 and is the frequency and initial phase of the third laser 61, signal E9 passes through the fourteenth Y-type optical coupler 62, the fifteenth Y-type optical coupler 63, the twelfth Y-type optical coupler 54, is reflected at the sixth online Faraday rotator 53, passes through the twelfth Y-type optical coupler 54 and the thirteenth Y-type optical coupler 55, reaches the ninth photodetector 57 to beat with signal E8, the beat signal is frequency-divided at the second frequency division module 58 and is input to the fourth servo control module 60 together with the reference signal of the third reference frequency source 7 for locking, and the output direct current error signal V e，3 into the servo control module, the expression of which is:

[0164]

[0165] When the fourth servo control module works in the locking state, V e，3 is close to 0, and the expression can be further written as:

[0166]

[0167] v2=v0+38MHz

[0168] The locked optical signal is Signal E after passing through the fourteenth Y-type optical coupler 62, the fifteenth Y-type optical coupler 63, the twelfth Y-type optical coupler 54, the sixth online Faraday rotator 53, the eleventh Y-type optical coupler 51, the second polarization controller 50, the optical fiber link and the fifth acousto-optic modulator 43 is recorded as E 10 , the expression of the signal is

[0169]

[0170] The signal E 10 passes through the tenth Y-type optical coupler 42, the fifth online Faraday rotator 41, the fourth online Faraday rotator 40, the ninth Y-type optical coupler 39, beats with signal E7 at the sixth photodetector 44, and the beat signal is recorded as E 11 , signal E 11 is transmitted to the first mixer 45 to mix with signal E6, and the mixed signal is recorded as E 12 , the expression of the signal is

[0171]

[0172]

[0173] The mixed signal E 12 is input to the third servo control module 47 together with the reference signal of the second reference frequency source 6 for locking, and the output direct current error signal V e，4The expression of the entering servo control module is:

[0174]

[0175] When the third servo control module works in the locking state, V e，4 is close to 0, and the expression can be further written as:

[0176]

[0177] The signal after locking is compensated to the fifth acousto-optic modulator 43, so as to compensate the phase noise introduced by the reference frequency source and the optical fiber link of the regenerative repeater end 2.

[0178] The regenerative repeater end 3:

[0179] In the regenerative repeater end 3, the received signal after transmission through the transmission link can be expressed as:

[0180]

[0181] The signal E 13 passes through the second polarization controller (50), the eleventh Y-type optical coupler 51, the sixth on-line Faraday rotator 53, the twelfth Y-type optical coupler 54, the thirteenth Y-type optical coupler 55, and reaches the ninth photodetector 57.

[0182] The optical signal emitted by the third laser 61 is The signal E9 passes through the fourteenth Y-type optical coupler 62, the fifteenth Y-type optical coupler 63, the twelfth Y-type optical coupler 54, is reflected at the sixth on-line Faraday rotator 53, passes through the twelfth Y-type optical coupler 54 and the thirteenth Y-type optical coupler 55, and reaches the ninth photodetector 57 to be combined with the signal E 13 The beat frequency is frequency-divisioned at the second frequency division module 58, and the beat frequency signal is input to the fourth servo control module 60 together with the reference signal of the third reference frequency source 7 to be locked, and the output direct current error signal V e，5 The expression of the entering servo control module is:

[0183]

[0184] When the fourth servo control module works in the locking state, V e，5 is close to 0, and the expression can be further written as:

[0185]

[0186] v2=v0+38MHz

[0187] The locked optical signal is The light signal is split into two paths at the fifteenth Y-type optical coupler 63 through the fourteenth Y-type optical coupler 62. One light signal is reflected at the sixth inline Faraday rotator 53 through the twelfth Y-type optical coupler 54, the fifteenth Y-type optical coupler 63, the fourteenth Y-type optical coupler 62, and reaches the tenth photodetector 64. The other light signal is split into two paths at the seventh inline Faraday rotator 67 through the seventh acousto-optic modulator 65 and the sixteenth Y-type optical coupler 66. One light signal is reflected, and the signal expression after the light signal is split into two paths again at the sixteenth Y-type optical coupler 66 is E 14 , which reaches the tenth photodetector 64 and beats with the signal E9. The beat signal is transmitted to the second mixer 72, and the beat signal is E 15 . The other light signal reaches the eleventh photodetector 71 and is E 16 . The signal expression is

[0188]

[0189]

[0190]

[0191] In the formula, is the phase noise introduced by the third reference frequency source 7.

[0192] The other light signal at the seventh inline Faraday rotator 67 passes through the seventh inline Faraday rotator 67, the eighth inline Faraday rotator 68, the seventeenth Y-type optical coupler 69, the eighth acousto-optic modulator 70, and the optical fiber link. The signal expression is E 17 . The signal expression is

[0193]

[0194] In the formula, is the initial phase of the eighth acousto-optic modulator 70, is the phase noise introduced by the optical fiber link. The signal E 17 passes through the third polarization controller 77, the eighteenth Y-type optical coupler 78, the ninth inline Faraday rotator 80, the nineteenth Y-type optical coupler 81, the twentieth Y-type optical coupler 82, and reaches the fourteenth photodetector 84.

[0195] The light signal emitted by the fourth laser 88 is In the formula, v3 and are the frequency and initial phase of the fourth laser 88. The signal E18 through the ninth on-line Faraday rotator 80, the nineteenth Y-type optical coupler 81, the twentieth Y-type optical coupler 82, and reaches the fourteenth photodetector 84 to be combined with the signal E 17 The beat frequency signal is input into the sixth servo control module 87 together with the reference signal of the fourth reference frequency source 8 after frequency division at the third frequency division module 85, and a direct current error signal V e，6 into the servo control module, and its expression is:

[0196]

[0197] When the sixth servo control module works in the locking state, V e，6 is close to 0, and the expression can be further written as:

[0198]

[0199] v3=v0-108MHz

[0200] The locked optical signal is The signal after passing through the twenty-first Y-type optical coupler 89, the nineteenth Y-type optical coupler 81, the ninth on-line Faraday rotator 80, the eighteenth Y-type optical coupler 78, the third polarization controller 77, the optical fiber link, and the eighth acousto-optic modulator 70 is denoted as E 19 , and the expression of the signal is

[0201]

[0202] The signal E 19 passes through the seventeenth Y-type optical coupler 69, the eighth on-line Faraday rotator 68, the seventh on-line Faraday rotator 67, the sixteenth Y-type optical coupler 66, and reaches the eleventh photodetector 71 to be combined with the signal E 16 The beat frequency signal is denoted as E 20 , and the signal E 20 is transmitted to the first mixer 45 to be combined with the signal E 15 The mixed signal is denoted as E 21 , and the expression of the signal is

[0203]

[0204]

[0205] The mixed signal E 21 is input into the fifth servo control module 74 together with the reference signal of the third reference frequency source 7 to be locked, and a direct current error signal Ve，7 The expression of the entering servo control module is:

[0206]

[0207] When the fifth servo control module works in the locking state, V e，7 is close to 0, and the expression can be further written as:

[0208]

[0209] The signal after locking is compensated to the eighth acousto-optic modulator 70, so as to compensate the phase noise introduced by the reference frequency source of the regenerative repeater end 3 and the optical fiber link.

[0210] The user end (4) is:

[0211] In the user end (4), the received signal after transmission through the transmission link can be expressed as:

[0212]

[0213] The signal E 22 Passes through the third polarization controller 77, the eighteenth Y-type optical coupler 78, the ninth online Faraday rotator 80, the nineteenth Y-type optical coupler 81, the twentieth Y-type optical coupler 82, and reaches the fourteenth photodetector 84.

[0214] The optical signal emitted by the fourth laser 88 is Passes through the twenty-first Y-type optical coupler 89, the nineteenth Y-type optical coupler 81, is reflected at the ninth online Faraday rotator 80, passes through the nineteenth Y-type optical coupler 81, the twentieth Y-type optical coupler 82, and reaches the fourteenth photodetector 84 and the signal E 22 The beat frequency, after the beat frequency signal is frequency-divided at the third frequency division module 85, is input to the sixth servo control module 87 together with the reference signal of the fourth reference frequency source 8 to be locked, and the output direct current error signal V e，8 The expression of the entering servo control module is:

[0215]

[0216] When the sixth servo control module works in the locking state, V e，8 is close to 0, and the expression can be further written as:

[0217]

[0218] v3=v0-108MHz

[0219] The optical signal after locking is The phase noise introduced by the reference frequency source and the optical fiber link in each station is compensated so that the phase remains stable.

[0220] Embodiment 2

[0221] Please refer to Figure 5 , Figure 5 The structure diagram of the embodiment of the optical frequency transfer regenerative relay structure level system of the application is shown in the figure. It can be seen from the figure that the super-long distance optical frequency transfer can be realized by alternately cascading the first regenerative relay end and the second regenerative relay end.

Claims

1. An optical frequency transfer system with regenerative repeater amplification comprising a local end (1) and a user end (4), said local end (1) and user end (4) being connected by a fiber link, characterized in that, N alternating regenerative repeaters are distributed on the optical fiber link, and N≥2; The local end (1) comprises a first reference frequency source (5), a first laser (11), a first Y-type optical coupler (12), a first online Faraday rotator (13), a second online Faraday rotator (14), a second Y-type optical coupler (15), a first acousto-optic modulator (16), a third Y-type optical coupler (17), a first photoelectric detector (18), a first servo control module (19), a first direct digital frequency synthesizer (20), a second acousto-optic modulator (21), and a second photoelectric detector (22); The first regenerative repeater (2) comprises a second reference frequency source (6), a first polarization controller (23), a third acousto-optic modulator (24), a fourth Y-type optical coupler (25), a third online Faraday rotator (26), a fifth Y-type optical coupler (27), a sixth Y-type optical coupler (28), a third photoelectric detector (29), a fourth photoelectric detector (30), a first frequency division module (31), a second servo control module (33), a second laser (34), a seventh Y-type optical coupler (35), an eighth Y-type optical coupler (36), a fifth photoelectric detector (37), a fourth acousto-optic modulator (38), a ninth Y-type optical coupler (39), a fourth online Faraday rotator (40), a fifth online Faraday rotator (41), a tenth Y-type optical coupler (42), a fifth acousto-optic modulator (43), a sixth photoelectric detector (44), a first frequency mixer (45), a third servo control module (47), a second direct digital frequency synthesizer (48), and a seventh photoelectric detector (49); The second regenerative repeater (3) comprises a third reference frequency source (7), a second polarization controller (50), an eleventh Y-type optical coupler (51), a sixth acousto-optic modulator (52), a sixth online Faraday rotator (53), a twelfth Y-type optical coupler (54), a thirteenth Y-type optical coupler (55), an eighth photoelectric detector (56), a ninth photoelectric detector (57), a second frequency division module (58), a fourth servo control module (60), a third laser (61), a fourteenth Y-type optical coupler (62), a fifteenth Y-type optical coupler (63), a tenth photoelectric detector (64), a seventh acousto-optic modulator (65), a sixteenth Y-type optical coupler (66), a seventh online Faraday rotator (67), an eighth online Faraday rotator (68), a seventeenth Y-type optical coupler (69), an eighth acousto-optic modulator (70), an eleventh photoelectric detector (71), a second frequency mixer (72), a fifth servo control module (74), a third direct digital frequency synthesizer (75), and a twelfth photoelectric detector (76).

2. The optical frequency transfer system of claim 1, wherein The first laser (11) emits a light signal to be transmitted into the second port of the first Y-type optical coupler (12), the first port of the first Y-type optical coupler (12) is connected with the first online Faraday rotator (13), the first online Faraday rotator (13) is connected with the second online Faraday rotator (14), the second online Faraday rotator (14) is connected with the first port of the second Y-type optical coupler (15), the second port of the second Y-type optical coupler (15) is connected with the first acousto-optic modulator (16), and the first acousto-optic modulator (16) is connected into the optical fiber link; The third port of the first Y-type optical coupler (12) is connected with the first port of the third Y-type optical coupler (17), the second port of the third Y-type optical coupler (17) is connected with the input end of the first photodetector (18), the output end of the first photodetector (18) is connected with the input end of the first reference frequency source (5) and the input end of the first servo control module (19) together, the output end of the first servo control module (19) is connected with the input end of the first direct digital frequency synthesizer (20), and the output end of the first direct digital frequency synthesizer (20) is connected with the radio frequency port of the first acousto-optic modulator (16); The third port of the third Y-type optical coupler (17) is connected with the second acousto-optic modulator (21), and the second acousto-optic modulator (21) is connected with the second photodetector (22); The first polarization controller (23) is connected with the first acousto-optic modulator (16) of the local end (1) through an optical fiber link, the first polarization controller (23) is connected with the second port of the fourth Y-type optical coupler (25), the third port of the fourth Y-type optical coupler (25) is connected with the third acousto-optic modulator (24); the first port of the fourth Y-type optical coupler (25) is connected with the third on-line Faraday rotator (26), the first port of the fifth Y-type optical coupler (27) is connected with the third port of the sixth Y-type optical coupler (28), the third port of the sixth Y-type optical coupler (28) is connected with the third photoelectric detector (29); the second port of the sixth Y-type optical coupler (28) is connected with the fourth photoelectric detector (30), the fourth photoelectric detector (30) is connected with the first frequency division module (31), the output of the first frequency division module (31) is input to the second servo control module (33) together with the second reference frequency source (6), the output of the second servo control module (33) is used for locking the second laser (34); the second laser (34) is connected with the third port of the seventh Y-type optical coupler (35), the first port of the seventh Y-type optical coupler (35) is connected with the first port of the eighth Y-type optical coupler (36), the second port of the eighth Y-type optical coupler (36) is connected with the second port of the fifth Y-type optical coupler (27); the third port of the eighth Y-type optical coupler (36) is connected with the fourth acousto-optic modulator (38), the second port of the fourth acousto-optic modulator (38) is connected with the second port of the ninth Y-type optical coupler (39), the first port of the Y-type optical coupler (39) is connected with the fourth on-line Faraday rotator (40), the fourth on-line Faraday rotator (40) is connected with the fifth on-line Faraday rotator (41), the first port of the tenth Y-type optical coupler (42) is connected with the third port of the seventh photoelectric detector (49); the second port of the seventh Y-type optical coupler (35) is connected with the fifth photoelectric detector (37); the third port of the ninth Y-type optical coupler (39) is connected with the sixth photoelectric detector (44);The output of the fifth photodetector (37) and the sixth photodetector (44) is connected to the input of the first frequency mixer (45), the output of which is input to the second reference frequency source (6) to the third servo control module (47), which is connected to the second direct digital frequency synthesizer (48), which is connected to the radio frequency port of the fifth acousto-optic modulator (43), the output of which is connected to the fiber link. The input end of the second polarization controller (50) is connected with the fifth acousto-optic modulator (43) of the first regenerative repeater (2) through an optical fiber link, the second polarization controller (50) is connected with the second port of the eleventh Y-type optical coupler (51), the third port of the eleventh Y-type optical coupler (51) is connected with the sixth acousto-optic modulator (52); the first port of the eleventh Y-type optical coupler (51) is connected with the sixth on-line Faraday rotator (53), the sixth on-line Faraday rotator (53) is connected with the first port of the twelfth Y-type optical coupler (54), the third port of the twelfth Y-type optical coupler (54) is connected with the first port of the thirteenth Y-type optical coupler (55), the second port of the thirteenth Y-type optical coupler (55) is connected with the eighth photodetector (56); the third port of the thirteenth Y-type optical coupler (55) is connected with the ninth photodetector (57), the ninth photodetector (57) is connected with the second frequency division module (58), the output of the second frequency division module (58) is input to the fourth servo control module (60) together with the third reference frequency source (7), the output of the fourth servo control module (60) is used for locking the third laser (61); the third laser (61) is connected with the second port of the fourteenth Y-type optical coupler (62), the first port of the fourteenth Y-type optical coupler (62) is connected with the first port of the fifteenth Y-type optical coupler (63), the second port of the fifteenth Y-type optical coupler (63) is connected with the second port of the twelfth Y-type optical coupler (54); the third port of the fifteenth Y-type optical coupler (63) is connected with the seventh acousto-optic modulator (65), the seventh acousto-optic modulator (65) is connected with the second port of the sixteenth Y-type optical coupler (66), the first port of the sixteenth Y-type optical coupler (66) is connected with the seventh on-line Faraday rotator (67), the seventh on-line Faraday rotator (67) is connected with the eighth on-line Faraday rotator (68), the eighth on-line Faraday rotator (68) is connected with the first port of the seventeenth Y-type optical coupler (69), the third port of the seventeenth Y-type optical coupler (69) is connected with the twelfth photodetector (76); the third port of the fourteenth Y-type optical coupler (62) is connected with the tenth photodetector (64); the third port of the sixteenth Y-type optical coupler (66) is connected with the eleventh photodetector (71);The output of the tenth photodetector (64) and the eleventh photodetector (71) is connected to the input of the second frequency mixer (72), the output of the second frequency mixer (72) is commonly input to the fifth servo control module (74) with the third reference frequency source (7), the fifth servo control module (74) is connected to the third direct digital frequency synthesizer (75), the third direct digital frequency synthesizer (75) is connected to the radio frequency port of the eighth acousto-optic modulator (70), and the output of the eighth acousto-optic modulator (70) is connected to the optical fiber link. The user terminal (4) comprises a fourth reference frequency source (8), a third polarization controller (77), an eighteenth Y-type optical coupler (78), a ninth acousto-optic modulator (79), a ninth online Faraday rotator (80), a nineteenth Y-type optical coupler (81), a twentieth Y-type optical coupler (82), a thirteenth photodetector (83), a fourteenth photodetector (84), a third frequency division module (85), a sixth servo control module (87), a fourth laser (88) and a twenty-first Y-type optical coupler (89); The input end of the third polarization controller (77) is connected with the output end of the acousto-optic modulator of the Nth regenerative repeater through an optical fiber link, the third polarization controller (77) is connected with the second port of the eighteenth Y-type optical coupler (78), the third port of the eighteenth Y-type optical coupler (78) is connected with the ninth acousto-optic modulator (79); the first port of the eighteenth Y-type optical coupler (78) is connected with the ninth online Faraday rotator (80), the ninth online Faraday rotator (80) is connected with the first port of the nineteenth Y-type optical coupler (81), the third port of the nineteenth Y-type optical coupler (81) is connected with the first port of the twentieth Y-type optical coupler (82), the third port of the twentieth Y-type optical coupler (82) is connected with the thirteenth photodetector (83); the second port of the twentieth Y-type optical coupler (82) is connected with the fourteenth photodetector (84), the fourteenth photodetector (84) is connected with the third frequency division module (85), the output of the third frequency division module (85) is output to the sixth servo control module (87) together with the fourth reference frequency source (8), the output of the sixth servo control module (87) is used for locking the fourth laser (88); the fourth laser (88) is connected with the first port of the twenty-first Y-type optical coupler (89), the third port of the twenty-first Y-type optical coupler (89) is connected with the second port of the nineteenth Y-type optical coupler (81), the signal transmitted by the second port of the twenty-first Y-type optical coupler (89) is the received signal.

3. The regenerative relay-amplified optical frequency transfer system of claim 1, wherein, The N regenerative repeaters are equidistantly distributed on the optical fiber link and are connected in an alternating cascade mode, so that the transmission of optical signals over a longer distance is realized.

4. An optical frequency transfer method of the optical frequency transfer system according to claim 2, characterized by, The method comprises the following steps: Local end: The optical signal to be transmitted is E0, where ω0and are the angular frequency and the initial phase, respectively, of the optical signal to be transmitted. After input through the second port of the first Y-type coupler (12), the signal is output to the first online Faraday rotator (13) through the first port; the signal is divided into two paths through the first online Faraday rotator (13), one path of the reflected light signal is input through the first port and output through the third port of the first Y-type optical coupler (12), and then the signal reaches the first photodetector (18) through the third Y-type optical coupler (17), and the signal is still recorded as E0; the other path of the transmitted light signal is sequentially input into the optical fiber link through the second online Faraday rotator (14), the second Y-type optical coupler (15) and the first acousto-optic modulator (16), and the signal is recorded as E1, and the expression is where ω1and is the frequency and initial phase of the radio frequency operation of the first acousto-optic modulator (16), is the phase noise introduced by the fiber link; The signal E1 is sequentially input into the fourth photodetector (30) through the first polarization controller (23), the fourth Y-type optical coupler (25), the third online Faraday rotator (26), the fifth Y-type optical coupler (27) and the sixth Y-type optical coupler (28); the light signal E2 emitted by the second laser (34), where ω2and are the frequency and initial phase of the second laser (34), The light signal E2 passes through the seventh Y-type optical coupler (35), the eighth Y-type optical coupler (36) and the fifth Y-type optical coupler (27), is reflected at the third online Faraday rotator (26), passes through the fifth Y-type optical coupler (27) and the sixth Y-type optical coupler (28), reaches the fourth photodetector (30) to beat with the signal E1, the beat signal is frequency-divided at the first frequency division module (31) and input to the second servo control module (33) together with the reference signal of the second reference frequency source (6) to be locked to -ω N , the output direct current error signal V e,0 , feedback control the second laser (34); When the second servo control module is working in the locked state, V e,0 is close to 0, i.e.: ω2= ω0+ ω1- ω N locked second laser output optical signal The signal after passing through the seventh Y-type optical coupler (35), the eighth Y-type optical coupler (36), the fifth Y-type optical coupler (27), the third inline Faraday rotator (26), the fourth Y-type optical coupler (25), the first polarization controller (23), the fiber link and the first acousto-optic modulator (16) is denoted as E3, and the signal expression is The signal E3 passes through the second Y-type optical coupler (15), the second on-line Faraday rotator (14), the first on-line Faraday rotator (13), the first Y-type optical coupler (12) and the third Y-type optical coupler (17), reaches the first photodetector (18) to beat with the signal E0, the beat signal is input to the first servo control module (19) to lock, the output direct current error signal V e,1 into the servo control module, whose expression is: V e,1 When the first servo control module is operating in the locked state, V e,1 When the first servo control module is operating in the locked state, V e,1 When the first servo control module is operating in the locked state, V e,1 When the first The phase noise introduced by the optical fiber link can be compensated by compensating the locked signal to the first acousto-optic modulator (16); First regenerative repeater (2): After transmission over the transmission link, the received signal E4 is represented as: The signal E4 passes through a first polarization controller (23), a fourth Y-type optical coupler (25), a third on-line Faraday rotator (26), a fifth Y-type optical coupler (27), a sixth Y-type optical coupler (28), and reaches a fourth photoelectric detector (30); The light signal E2 emitted by the second laser (34) passes through the seventh Y-type optical coupler (35), the eighth Y-type optical coupler (36) and the fifth Y-type optical coupler (27), is reflected at the third on-line Faraday rotator (26), passes through the fifth Y-type optical coupler (27) and the sixth Y-type optical coupler (28), reaches the fourth photoelectric detector (30) to beat with the signal E4, and the beat signal is divided in frequency at the first frequency division module (31) and then input to the second servo control module (33) together with the reference signal of the second reference frequency source (6) to be locked to -ω N , the output direct-current error signal V e,2 enters the servo control module, and the expression thereof is: V e,2 When the second servo control module is operating in the locked state, V e,2 When the second servo control module is operating in the locked state, V e,2 When the second servo control module is operating in the locked state, V e,2 When the second ω2= ω0+ ω1- ω N The locked optical signal is After passing through the seventh Y-type optical coupler (35), the optical signal is divided into two paths at the eighth Y-type optical coupler (36). One path of the optical signal passes through the fifth Y-type optical coupler (27), is reflected at the third online Faraday rotator (26), passes through the fifth Y-type optical coupler (27), the eighth Y-type optical coupler (36), and the seventh Y-type optical coupler (35), and reaches the fifth photodetector (37). The signal expression is still E2. The other path of the optical signal passes through the fourth acousto-optic modulator (38) and the ninth Y-type optical coupler (39), is divided into two paths at the fourth online Faraday rotator (40), one path of the optical signal is reflected, passes through the ninth Y-type optical coupler (39), and is again divided into two paths. One path of the optical signal passes through the fourth acousto-optic modulator (38), the eighth Y-type optical coupler (36), and the seventh Y-type optical coupler (35) after which the signal is denoted as E5. The signal E5 reaches the fifth photodetector (37) and beats with the signal E2. The beat signal is transmitted to the first frequency mixer (45) and is denoted as E6. The other path of the optical signal reaches the sixth photodetector (44) and is denoted as E7. The signal expression is In the formula, ω1 is also the frequency at which the fourth acousto-optic modulator (38) operates at radio frequency, and is consistent with the frequency shift direction of the first acousto-optic modulator (16), is the phase noise introduced by the second reference frequency source (6); Another optical signal at the fourth on-line Faraday rotator (40) passes through the fourth on-line Faraday rotator (40), a fifth on-line Faraday rotator (41), a tenth Y-type optical coupler (42), a fifth acousto-optic modulator (43), and an optical fiber link, and the signal expression is E8, which is In the formula, ω1 and is the frequency and initial phase of the fifth acousto-optic modulator (43) operating at radio frequency, and the frequency shift direction of the first acousto-optic modulator (16) is opposite, is the phase noise introduced by the optical fiber link; The signal E8 passes through a second polarization controller (50), an eleventh Y-type optical coupler (51), a sixth on-line Faraday rotator (53), a twelfth Y-type optical coupler (54), a thirteenth Y-type optical coupler (55), and reaches a ninth photoelectric detector (57); The optical signal emitted by the third laser (61) is where ω3 and is the frequency and initial phase of the third laser (61), signal E9 passes through the fourteenth Y-type optical coupler (62), the fifteenth Y-type optical coupler (63), the twelfth Y-type optical coupler (54), is reflected at the sixth on-line Faraday rotator (53), passes through the twelfth Y-type optical coupler (54), the thirteenth Y-type optical coupler (55), reaches the ninth photodetector (57) to beat with signal E8, the beat signal is frequency-divided at the second frequency division module (58) and input to the fourth servo control module (60) together with the reference signal of the third reference frequency source (7) to be locked to ω N , the output direct current error signal V e,3 enters the servo control module, and its expression is: V e,3 When the fourth servo control module is working in the locked state, V e,3 When the fourth servo control module is working in the locked state, V e,3 When the fourth servo control module is working in the locked state, V e,3 When the fourth ω3=ω0+ω1 The locked optical signal is The signal after passing through the fourteenth Y-type optical coupler (62), the fifteenth Y-type optical coupler (63), the twelfth Y-type optical coupler (54), the sixth in-line Faraday rotator (53), the eleventh Y-type optical coupler (51), the second polarization controller (50), an optical fiber link, and the fifth acousto-optic modulator (43) is denoted as E 10 The signal expression is The signal E 10 passes through the tenth Y-type optical coupler (42), the fifth on-line Faraday rotator (41), the fourth on-line Faraday rotator (40), the ninth Y-type optical coupler (39), and beats with the signal E7 at the sixth photodetector (44). The beat signal is denoted as E 11 , the signal E 11 is transmitted to the first mixer (45) to mix with the signal E6. The mixed signal is denoted as E 12 , and the signal expression is Mixing signal E 12 The reference signal of the second reference frequency source (6) is input to the third servo control module (47) for locking, and the output direct current error signal V e,4 into the servo control module, whose expression is: V e,4 When the third servo control module is working in the locked state, V e,4 When the third servo control module is working in the locked state, V e,4 When the third servo control module is working in the locked state, V e,4 When the third Compensating the locked signal to the fifth acousto-optic modulator (43) can compensate the phase noise introduced by the reference frequency source and the optical fiber link of the regenerative repeater (2); Second regenerative repeater (3): After transmission through the transmission link, the received signal in the regenerative repeater (3) can be expressed as: The signal E 13 passes through the second polarization controller (50), the eleventh Y-type optical coupler (51), the sixth inline Faraday rotator (53), the twelfth Y-type optical coupler (54), the thirteenth Y-type optical coupler (55), and reaches the ninth photodetector (57); The light signal emitted by the third laser (61) is Signal E9 passes through the fourteenth Y-type optical coupler (62), the fifteenth Y-type optical coupler (63), the twelfth Y-type optical coupler (54), is reflected at the sixth on-line Faraday rotator (53), passes through the twelfth Y-type optical coupler (54) and the thirteenth Y-type optical coupler (55), and reaches the ninth photodetector (57) to be combined with signal E 13 The beat frequency, after the beat frequency signal is frequency-divided at the second frequency division module (58), is input to the fourth servo control module (60) together with the reference signal of the third reference frequency source (7) to be locked to ω N The output direct current error signal V e,5 enters the servo control module, and the expression is: V e,5 When the fourth servo control module is working in the locked state, V When the fourth servo control module is working in the locked state, V When the fourth servo control module is working in the locked state, V When the fourth servo control module is working in the locked state, V When the fourth ω3=ω0+ω1 The locked optical signal is After the fourteenth Y-type optical coupler (62), the optical signal is divided into two paths at the fifteenth Y-type optical coupler (63), one path of the optical signal passes through the twelfth Y-type optical coupler (54), is reflected at the sixth online Faraday rotator (53), passes through the twelfth Y-type optical coupler (54), the fifteenth Y-type optical coupler (63), the fourteenth Y-type optical coupler (62), and reaches the tenth photodetector (64); the other path of the optical signal passes through the seventh acousto-optic modulator (65), the sixteenth Y-type optical coupler (66), is divided into two paths at the seventh online Faraday rotator (67), one path of the optical signal is reflected, the optical signal is again divided into two paths at the sixteenth Y-type optical coupler (66), one path of the optical signal passes through the seventh acousto-optic modulator (65), the fifteenth Y-type optical coupler (63), the fourteenth Y-type optical coupler (62), and the signal expression after the above is denoted as E 14 , reaches the tenth photodetector (64) and beats with the signal E9, the beat signal is transmitted to the second frequency mixer (72), the beat signal is denoted as E 15 , the other path of the optical signal reaches the eleventh photodetector (71) and is denoted as E 16 , and the signal expression is where ω1is the frequency at which the seventh acousto-optic modulator (65) operates, but in the opposite direction to the frequency shift of the first acousto-optic modulator (16), is the phase noise introduced by the third reference frequency source (7); The other optical signal at the seventh on-line Faraday rotator (67) passes through the seventh on-line Faraday rotator (67), the eighth on-line Faraday rotator (68), the seventeenth Y-type optical coupler (69), the eighth acousto-optic modulator (70) and the optical fiber link, and the signal expression is E 17 , and the signal expression is ω1 is the frequency of the eighth acousto-optic modulator (70) operating at radio frequency, and is consistent with the frequency shift direction of the first acousto-optic modulator (16), is the initial phase of the eighth acousto-optic modulator (70), is the phase noise introduced by the optical fiber link; the signal E 17 passes through the third polarization controller (77), the eighteenth Y-type optical coupler (78), the ninth in-line Faraday rotator (80), the nineteenth Y-type optical coupler (81), the twentieth Y-type optical coupler (82), and reaches the fourteenth photodetector (84); The optical signal emitted by the fourth laser (88) is where ω4 and is the frequency and initial phase of the fourth laser (88), and the signal E 18 passes through the twenty-first Y-type optical coupler (89), the nineteenth Y-type optical coupler (81), is reflected at the ninth on-line Faraday rotator (80), passes through the nineteenth Y-type optical coupler (81), the twentieth Y-type optical coupler (82), and reaches the fourteenth photodetector (84) to be combined with the signal E 17 The beat frequency, after being frequency-divided at the third frequency-division module (85), is input together with the reference signal of the fourth reference frequency source (8) to the sixth servo control module (87) to be locked to -ω N , and the output direct-current error signal V e,6 enters the servo control module, and its expression is: V e,6 When the sixth servo control module is working in the locked state, V When the sixth servo control module is working in the locked state, V When the sixth servo control module is working in the locked state, V When the sixth servo control module is working in the locked state, V When the sixth servo control ω4= ω0+ ω1- ω N The locked optical signal is The signal after the twenty-first Y-type optical coupler (89), the nineteenth Y-type optical coupler (81), the ninth in-line Faraday rotator (80), the eighteenth Y-type optical coupler (78), the third polarization controller (77), the optical fiber link, the eighth acousto-optic modulator (70) is denoted as E 19 The signal expression is The signal E 19 passes through the seventeenth Y-type optical coupler (69), the eighth in-line Faraday rotator (68), the seventh in-line Faraday rotator (67), the sixteenth Y-type optical coupler (66), and is combined with the signal E 16 at the eleventh photodetector (71) 20 , the signal E 20 is transmitted to the first mixer (45) and is combined with the signal E 15 , the mixed signal is denoted as E 21 , the signal expression is: Mixing signal E 21 The reference signal of the third reference frequency source (7) is input to the fifth servo control module (74) for locking, and the output direct current error signal V e,7 into the servo control module, whose expression is: V e,7 When the fifth servo control module is working in the locked state, V e,7 When the fifth servo control module is working in the locked state, V e,7 When the fifth servo control module is working in the locked state, V e,7 When the fifth servo control Compensating the locked signal to the eighth acousto-optic modulator (70) can compensate the phase noise introduced by the reference frequency source and the optical fiber link of the regenerative repeater (3); User terminal (4): In the user terminal (4), the signal E received after transmission over the transmission link is represented as: 22 E = E0+ n (1) The signal E 22 through a third polarization controller (77), an eighteenth Y-type optical coupler (78), a ninth in-line Faraday rotator (80), a nineteenth Y-type optical coupler (81), a twentieth Y-type optical coupler (82), to a fourteenth photodetector (84); The optical signal emitted by the fourth laser (88) is Through the twenty-first Y-type optical coupler (89), the nineteenth Y-type optical coupler (81), reflected at the ninth on-line Faraday rotator (80), through the nineteenth Y-type optical coupler (81), the twentieth Y-type optical coupler (82), to the fourteenth photodetector (84) and the signal E 22 The beat frequency, after the beat frequency signal is frequency-divided at the third frequency division module (85), is input together with the reference signal of the fourth reference frequency source (8) to the sixth servo control module (87) to be locked to -ω N , the output direct current error signal V e,8 into the servo control module, the expression of which is: V e,8 When the sixth servo control module is working in the locked state, V e,8 When the sixth servo control module is working in the locked state, V e,8 When the sixth servo control module is working in the locked state, V e,8 When the sixth servo control ω4= ω0+ ω1- ω N The locked optical signal is Compensate the phase noise introduced by the reference frequency source and the fiber link in each station, so that the phase stable optical frequency signal is obtained at the user end.

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